Fine materials generated from mining activities are often found well-dispersed in aqueous environments, such as wastewater. The finely dispersed materials may include such solids as various types of clay materials, recoverable materials, fine sand and silt. Separating these materials from the aqueous environment can be difficult, as they tend to retain significant amounts of water, even when separated out, unless special energy-intensive dewatering processes or long-term settling practices are employed.
An example of a high volume water consumption process is the processing of naturally occurring ores. During the processing of such ores, colloidal particles, such as clay and mineral fines, are released into the aqueous phase often due to the introduction of mechanical shear associated with the hydrocarbon-extraction process. In addition to mechanical shear, alkali water is sometimes added during extraction, creating an environment more suitable for colloidal suspensions. A common method for disposal of the resulting “tailing” solutions, which contain fine colloidal suspensions of clay and minerals, water, sodium hydroxide and small amounts of remaining hydrocarbon, is to store them in “tailings ponds.” These ponds take years to settle out the contaminating fines, posing severe environmental challenges. Tailings ponds or similar liquid retention areas can contain aqueous suspensions of fine particles from mining operations and other industrial operations, for example fine coal particles from coal mining and fly ash from coal combustion, with the potential for environmental damage and catastrophic leakage. It is desirable to identify a method for treating tailings from mining operations to reduce the existing tailings ponds, and/or to prevent their further expansion.
Certain mining processes use a large volume of water, placing strains on the local water supply. It would be advantageous, therefore, to reuse the water from tailings streams, so that there is less need for fresh water in the beneficiation process. In addition, certain mining processes can create waste streams of large-particle inorganic solids. This residue is typically removed in initial separation phases of processing due to its size, insolubility and ease of sequestering. Disposal or storage of this waste material represents a problem for the mining industry. It would be advantageous to modify this material so that it could be useful in-situ, for example as part of a treatment for the mining wastewater.
A typical approach to consolidating fine materials dispersed in water involves the use of coagulants or flocculants. This technology works by linking together the dispersed particles by use of multivalent metal salts (such as calcium salts, aluminum compounds or the like) or high molecular weight polymers such as partially hydrolyzed polyacrylamides. With the use of these agents, there is an overall size increase in the suspended particle mass; moreover, their surface charges are neutralized, so that the particles are destabilized. The overall result is an accelerated sedimentation of the treated particles. Following the treatment, though, a significant amount of water remains trapped with the sedimented particles. These technologies typically do not release enough water from the sedimented material that the material becomes mechanically stable. In addition, the substances used for flocculation/coagulation may not be cost-effective, especially when large volumes of wastewater require treatment, in that they require large volumes of flocculant and/or coagulant. While ballasted flocculation systems have also been described, these systems are inefficient in sufficiently removing many types of fine particles, such as those fine particles that are produced in wastewater from mining processes.
There remains an overall need in the art, therefore, for a treatment system that removes suspended particles from a fluid solution quickly, cheaply, and with high efficacy. It is also desirable that the treatment system yields a recovered (or recoverable) solid material that retains minimal water, so that it can be readily processed into a substance that is mechanically stable. It is further desirable that the treatment system yields clarified water that can be readily recycled for further industrial purposes.
An additional need in the art pertains to the management of existing tailings ponds. In their present form, they are environmental liabilities that may require extensive clean-up efforts in the future. It is desirable to prevent their expansion. It is further desirable to improve their existing state, so that their contents settle more efficiently and completely. A more thorough and rapid separation of solid material from liquid solution in the tailings pond could allow retrieval of recyclable water and compactable waste material, with an overall reduction of the footprint that they occupy.